In an extruder-type slipform casting process, the concrete mix is extruded with the help of auger feeders into a mold or through nozzles, whereby the casting machine is propelled along the casting bed by the reaction forces imposed on the auger feeders. The ready-cast product remains on the casting bed. The quality of the manufactured concrete product is affected by the adjustments of the casting machine and degree of wear in its components. The compaction of the concrete product may be very thorough even when the top surface of the product remains short of its nominal height or has an undulating upper profile.
Patent publication FI 80,845, for instance, describes a concrete mix compaction method. This approach, however, lacks a technique capable of securing the true straightness and correct height of the top surface in the product being made. After a sufficiently large portion of the cross section in the concrete product has reached a satisfactory degree of compaction, the extrusion force exerted on the cross section of the product exceeds the travel resistance imposed on the machine making it to proceed. Herein, the top surface of the concrete product may remain filled under the nominal height or assume an undulating profile notwithstanding the acceptable degree of compaction.
In the casting machine, the concrete mix feed trough functions as a flow guide for the concrete mix so as to form a portion of the auger feeder casing, whereby the length of the trough can be adjusted so as to control the flow of the concrete mix into the cross section of the product being cast. Generally, the length of the concrete mix feed trough is set separately for each kind of concrete mix to be cast. Such an adjustment is made on a one-time basis without later correction. Disadvantageously, however, the flow of the concrete mix subjects the feed trough to a wear particularly at the downstream end thereof. The wear progresses rapidly so far as to affect the flow of the concrete mix and, thereby, the filling of the concrete product cross section. As soon as the top surface of the cast product is found to be defectively filled, the feed trough must be replaced or the worn portion thereof otherwise repaired.